Testing gravitational parity violation with coincident gravitational waves and short gamma-ray bursts

TL;DR

This paper proposes a novel method to test gravitational parity violation by comparing distance measurements from gravitational waves and gamma-ray bursts, potentially revealing new physics beyond general relativity.

Contribution

It introduces a new observational test for gravitational parity violation using coincident GW and gamma-ray burst data, improving sensitivity over existing stationary constraints.

Findings

Ground-based detectors can measure source distance accurately.

Electromagnetic redshift measurements provide independent distance estimates.

The method is sensitive to Chern-Simons gravity, surpassing current constraints.

Abstract

Gravitational parity violation is a possibility motivated by particle physics, string theory and loop quantum gravity. One effect of it is amplitude birefringence of gravitational waves, whereby left and right circularly-polarized waves propagate at the same speed but with different amplitude evolution. Here we propose a test of this effect through coincident observations of gravitational waves and short gamma-ray bursts from binary mergers involving neutron stars. Such gravitational waves are highly left or right circularly-polarized due to the geometry of the merger. Using localization information from the gamma-ray burst, ground-based gravitational wave detectors can measure the distance to the source with reasonable accuracy. An electromagnetic determination of the redshift from an afterglow or host galaxy yields an independent measure of this distance. Gravitational parity violation would manifest itself as a discrepancy between these two distance measurements. We exemplify such a test by considering one specific effective theory that leads to such gravitational parity-violation, Chern-Simons gravity. We show that the advanced LIGO-Virgo network and all-sky gamma-ray telescopes can be sensitive to the propagating sector of Chern-Simons gravitational parity violation to a level roughly two orders of magnitude better than current stationary constraints from the LAGEOS satellites.